Support for fields in entities using Inline Entity Form

I refactored the hook_form_alter() so that I could share most of the code/logic in hook_inline_entity_form_entity_form_alter().

I also refactored the tests, since they're identical, expect for the path to add the test node. So these are now scenario outlines in the main test.

So far, this works nicely for content-types that use IEF to auto-create ECK entities. However, we'll need to make this recursive, since the ECK bundles could themselves include an IEF.

It turns out that this already works with multi-level IEF fields. I added a test for good measure.

Automatically closed - issue fixed for 2 weeks with no activity.